\documentclass{standalone}
\usepackage{ctex}
\usepackage{bytefield}

\begin{document}
\begin{bytefield}[bitwidth=1.1em]{32}
  \\
  \\
  \bitheader{0-31} \\
  \begin{rightwordgroup}{TCP \\ Header}
    \bitbox{16}{source port} & \bitbox{16}{destination port} \\
    \bitbox{32}{sequence number} \\
    \bitbox{32}{acknowledgment number} \\
    \bitbox{4}{offset} & \bitbox{4}{reserverd} & \bitbox{8}{tcp flags} & \bitbox{16}{window} \\
    \bitbox{16}{checksum} & \bitbox{16}{urgent pointer}
  \end{rightwordgroup} \\
  \begin{rightwordgroup}{TCP \\ Options}
    \begin{leftwordgroup}{Natcap \\ Option}
      \bitbox{8}{code=0x99} & \bitbox{8}{length=14} & \bitbox{8}{type=3(user)} & \bitbox{8}{encryption bits} \\
      \bitbox{32}{ user hash} \\
      \bitbox{8}{mac byte} & \bitbox{8}{mac byte} & \bitbox{8}{mac byte} &  \bitbox{8}{mac byte} \\
      \bitbox{8}{mac byte} & \bitbox{8}{mac byte} & \bitbox{16}{...}
    \end{leftwordgroup} \\
    \bitbox{32}{{ ... }other tcp options{ ... }}
  \end{rightwordgroup} \\
  \\
\end{bytefield}
\end{document}
